JP7236038B2 - vehicle steering system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system capable of realizing automatic steering control for automatically controlling a steering angle and manual steering control (assist control) for manually controlling a steering angle using the same electric motor.

Japanese Unexamined Patent Application Publication No. 2002-200002 discloses a vehicle steering system that can realize automatic steering control for automatically controlling a steering angle and manual steering control using the same actuator (electric motor). In the invention described in Patent Document 1, the steering torque to be applied to the steering shaft by the actuator (hereinafter referred to as target actuator torque _Tt ) is expressed by the following equation (a).

T _t = K _asst · T _asst + K _auto · T _auto (a)
In the above equation (a), T _asst is a target assist torque, T _auto is a target steering torque for performing automatic steering control (hereinafter referred to as target automatic steering torque), and K _asst and K _auto are weights. is the coefficient. The actuator is controlled to produce a torque that matches the target actuator torque _Tt .

During manual steering control, K _auto is zero, so T _t =K _asst ·T _asst . Further, during manual steering control, the coefficient K _asst is set to 1, so that T _t =T _asst . During automatic steering control, the target actuator torque _Tt is calculated based on the above equation (a). During the automatic steering control, the steering torque is 0 unless the steering operation is applied by the driver, except when the automatic steering control is started and ended. Therefore, the target assist torque T _asst is 0. In addition, since the coefficient K _auto is set to 1 during automatic steering control, T _t =T _auto .

In the invention described in Patent Document 1, transition control for transitioning from automatic steering control to manual steering control is started when steering intervention is detected during automatic steering control. In this transition control, the value of K _auto is decreased by a predetermined value _K1 and the value of K _asst is increased by a predetermined value _K2 every time a predetermined time elapses. However, when the value of K _auto falls below 0, K _auto is fixed at 0, and when the value of K _asst exceeds 1, K _asst is fixed at 1. Then, the updated K _auto and K _asst are used to calculate the target actuator torque _Tt , and the actuator is controlled so that the actuator generates a torque that matches the calculated target actuator torque _Tt . Thus, when K _auto has a value of 0 and K _asst has a value of 1, transition control ends.

Japanese Patent Application Laid-Open No. 2004-256076

In the transition control described in Patent Document 1, the value of K _auto is gradually decreased over time, and the value of K _asst is gradually increased over time. Then, when the value of K _auto becomes 0 and the value of K _asst becomes 1, transition control ends. As a result, fluctuations in the target actuator torque _Tt can be suppressed when the automatic steering control is canceled, so that the discomfort felt by the driver can be reduced. However, in the invention described in Patent Document 1, the time from the start to the end of the transition control (transition control time) is always constant, so the transition control time cannot be changed by the driver's steering operation. . Therefore, for example, in an emergency, it may not be possible to rapidly switch from automatic steering control to manual steering control.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a vehicle steering system capable of performing automatic steering control and manual steering control using the same electric motor by a new method, and capable of smoothly adjusting the degrees of automatic steering and manual steering. to provide.

A vehicle steering system according to an embodiment of the present invention includes an electric motor that applies a steering force to a steering mechanism of a vehicle, a first setting section that sets a target assist torque corresponding to the steering torque, and a target steering angle. a second setting unit for setting an angle control target torque for making the angular deviation from the actual steering angle close to zero; and a limit processing unit for limiting the angle control target torque set by the second setting unit. a first calculation unit for calculating a target automatic steering torque using the angle control target torque after the limit processing by the limit processing unit; and changing the target automatic steering torque and the target assist torque in accordance with a driver input. and a second calculation unit for calculating a target motor torque, which is a target value of the motor torque of the electric motor, by performing weighted addition according to the value to be calculated.

According to this configuration, a vehicle steering system is obtained in which automatic steering control and manual steering control can be performed using the same electric motor by a novel method. Further, according to this configuration, a vehicle steering system is obtained that enables seamless and quick switching from automatic steering control to manual steering control, or vice versa, while changing the weighting amount of each control.

In one embodiment of the present invention, the limit processing section is configured to limit the target torque for angle control set by the second setting section between a predetermined upper limit value and a predetermined lower limit value. there is

In one embodiment of the present invention, the second setting unit includes a feedback control unit for bringing the angular deviation closer to zero, and the limit processing unit, based on a value that changes according to driver input, The target torque for angle control set by the second setting section is limited by controlling the feedback gain of the feedback control section.

In one embodiment of the invention, the value that varies according to the driver input is the steering torque or the angular deviation.

In one embodiment of the present invention, the value that varies according to the driver's input is the steering torque or the angular deviation, and the value that varies according to the driver's input used in the second computing section and the limit process It is different from the value that changes according to the driver input used in the section.

The above and further objects, features and effects of the present invention will be made clear by the following description of embodiments with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering system that is an embodiment of a vehicle steering system according to the present invention. FIG. 2 is a block diagram for explaining the electrical configuration of the motor control ECU. FIG. 3 is a graph showing a setting example of the target assist torque Tm _,mc with respect to the steering torque _Td . FIG. 4 is a block diagram showing the configuration of the angle control section. FIG. 5 is a block diagram showing the configuration of the compensation target load estimator. FIG. 6 is a schematic diagram showing a configuration example of a physical model of the electric power steering system. FIG. 7 is a block diagram showing the configuration of the disturbance torque estimator. FIG. 8 is a block diagram showing the configuration of the shared control section. FIG. 9 is an explanatory diagram for explaining the operation of the limiter. FIG. 10 is an explanatory diagram for explaining the operation of the β calculator. FIG. 11 is a graph showing a setting example of the proportional gain K _P with respect to the steering torque absolute value |T _d |. FIG. 12 is a graph showing a setting example of the differential gain K _D with respect to the steering torque absolute value |T _d |.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering system that is an embodiment of a vehicle steering system according to the present invention.

This electric power steering system (EPS) 1 is a column-type EPS in which an electric motor and a speed reducer are arranged in a column portion.

An electric power steering system 1 includes a steering wheel (steering wheel) 2 as a steering member for steering a vehicle, a steering mechanism 4 for steering steered wheels 3 in conjunction with the rotation of the steering wheel 2, and a driving mechanism. and a steering assist mechanism 5 for assisting a person's steering. The steering wheel 2 and steering mechanism 4 are mechanically connected via a steering shaft 6 and an intermediate shaft 7 .

Steering shaft 6 includes an input shaft 8 connected to steering wheel 2 and an output shaft 9 connected to intermediate shaft 7 . The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable.

A torque sensor 12 is arranged near the torsion bar 10 . The torque sensor 12 detects steering torque (torsion bar torque) _Td applied to the steering wheel 2 based on relative rotational displacement amounts of the input shaft 8 and the output shaft 9 . In this embodiment, the steering torque _Td detected by the torque sensor 12 is, for example, a positive value for torque for steering to the left and a negative value for torque for steering to the right. , and the larger the absolute value, the larger the magnitude of the steering torque _Td .

The steering mechanism 4 is a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steering shaft. The steered wheels 3 are connected to each end of the rack shaft 14 via tie rods 15 and knuckle arms (not shown). The pinion shaft 13 is connected to the intermediate shaft 7 . The pinion shaft 13 rotates in conjunction with steering of the steering wheel 2 . A pinion 16 is connected to the tip of the pinion shaft 13 .

The rack shaft 14 extends linearly along the left-right direction of the vehicle. A rack 17 that meshes with the pinion 16 is formed in the axially intermediate portion of the rack shaft 14 . The pinion 16 and rack 17 convert the rotation of the pinion shaft 13 into axial movement of the rack shaft 14 . By moving the rack shaft 14 in the axial direction, the steerable wheels 3 can be steered.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and intermediate shaft 7 . Rotation of the pinion shaft 13 is converted into axial movement of the rack shaft 14 by the pinion 16 and the rack 17 . As a result, the steerable wheels 3 are steered.

The steering assist mechanism 5 includes an electric motor 18 for generating a steering assist force (assist torque) and a speed reducer 19 for amplifying the output torque of the electric motor 18 and transmitting it to the steering mechanism 4 . The speed reducer 19 comprises a worm gear mechanism including a worm gear 20 and a worm wheel 21 meshing with the worm gear 20 . The speed reducer 19 is accommodated in a gear housing 22 as a transmission mechanism housing. In the following, the reduction ratio (gear ratio) of the speed reducer 19 may be represented by N. The reduction ratio N is defined as the ratio ωw _g /ω _{ww of the angular speed ω wg of} the worm gear 20 to the angular speed ω _ww of the worm wheel 21 .

The worm gear 20 is rotationally driven by the electric motor 18 . Also, the worm wheel 21 is connected to the output shaft 9 so as to be rotatable together.

When the worm gear 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven, motor torque is applied to the steering shaft 6, and the steering shaft 6 (output shaft 9) rotates. Rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7 . Rotation of the pinion shaft 13 is converted into axial movement of the rack shaft 14 . As a result, the steerable wheels 3 are steered. That is, by rotationally driving the worm gear 20 with the electric motor 18, the steering assistance with the electric motor 18 and the steering of the steerable wheels 3 become possible. The electric motor 18 is provided with a rotation angle sensor 23 for detecting the rotation angle of the rotor of the electric motor 18 .

The torque applied to the output shaft 9 (an example of the object to be driven by the electric motor 18) includes motor torque by the electric motor 18 and disturbance torque other than the motor torque. The disturbance torque T _lc other than the motor torque includes steering torque T _d , road load torque (road surface reaction torque) T _rl , friction torque T _f and the like.

The steering torque T _d is torque applied to the output shaft 9 from the steering wheel 2 side due to the force applied to the steering wheel 2 by the driver or the inertial force of the steering wheel 2 .

The road load torque _Trl is torque applied from the road surface side to the output shaft 9 via the steerable wheels 3 and the rack shaft 14 due to self-aligning torque generated in tires, forces generated by the suspension and tire wheel alignment, and the like. .

The friction torque _Tf is torque applied to the output shaft 9 by friction generated in the torque transmission path from the torsion bar 10 to the tire. The friction torque _Tf includes the torque applied to the output shaft 9 by the friction between the worm wheel 21 and the worm gear 20 and the friction of the rack and pinion mechanism.

In this embodiment, the torque obtained by subtracting the steering torque T _d or the steering torque T _d′ compensated for the influence of the inertial force of the steering wheel 2 from the disturbance torque T _lc other than the motor torque is the angle control unit 42 (see FIG. 2) is the load to be compensated for the angle control target torque Tm _,ac (compensation target load) _Tle . Therefore, in this embodiment, the load to be compensated _Tle includes the road load torque (road surface reaction torque) _Trl and the friction torque _Tf . Hereinafter, the value (T _le /N) obtained by dividing the compensation target load T _le by the speed reduction ratio N of the speed reducer 19 will be represented by T _lem .

The vehicle includes a vehicle speed sensor 24 for detecting the vehicle speed V, a CCD (Charge Coupled Device) camera 25 for photographing the road in front of the vehicle, a GPS (Global Positioning System) 26 for detecting the position of the vehicle, A radar 27 for detecting road shapes and obstacles and a map information memory 28 for storing map information are mounted.

The CCD camera 25, GPS 26, radar 27, and map information memory 28 are connected to a host ECU (Electronic Control Unit) 201 for performing automatic support control and automatic driving control. Based on the information and map information obtained by the CCD camera 25, GPS 26 and radar 27, the host ECU 201 recognizes the surrounding environment, estimates the position of the vehicle, and plans routes, and determines control target values for steering and drive actuators. .

In this embodiment, the host ECU 201 sets a target steering angle θ _cmda for automatic steering. In this embodiment, the automatic steering control is, for example, control for running the vehicle along the target trajectory. The target steering angle θ _cmda is a target value of the steering angle for automatically driving the vehicle along the target track. Since the processing for setting the target steering angle θ _cmda is well known, detailed description thereof will be omitted here. In this embodiment, the rotation angle of the output shaft 9 is called "steering angle".

The target steering angle θ _cmda set by the host ECU 201 is given to the motor control ECU 202 via the in-vehicle network. The steering torque T _d detected by the torque sensor 12 , the output signal of the rotation angle sensor 23 , and the vehicle speed V detected by the vehicle speed sensor 24 are input to the motor control ECU 202 . The motor control ECU 202 controls the electric motor 18 based on these input signals and information given from the host ECU 201 .

FIG. 2 is a block diagram for explaining the electrical configuration of the motor control ECU 202. As shown in FIG.

The motor control ECU 202 includes a microcomputer 40, a drive circuit (inverter circuit) 31 that is controlled by the microcomputer 40 and supplies power to the electric motor 18, and a current flowing through the electric motor 18 (hereinafter referred to as "motor current I"). ) and a current detection circuit 32 for detecting the current.

The microcomputer 40 has a CPU and memory (ROM, RAM, non-volatile memory, etc.), and functions as a plurality of functional processing units by executing predetermined programs. The plurality of functional processing units include an assist control unit (assist map) 41, an angle control unit (Angle controller) 42, a compensation target load estimation unit 43, a shared control unit (shared control) 44, a target motor current A calculation unit 45 , a current deviation calculation unit 46 , a PI control unit 47 , a PWM (Pulse Width Modulation) control unit 48 , a rotation angle calculation unit 49 and a reduction ratio division unit 50 are included.

The assist control section 41 is an example of the first setting section of the present invention. The angle control section 42 is an example of the second setting section of the present invention. The shared control section 44 is an example of the first calculation section and the second calculation section of the present invention.

The rotation angle calculator 49 calculates the rotor rotation angle _θm of the electric motor 18 based on the output signal of the rotation angle sensor 23 . A reduction ratio division unit 50 divides the rotor rotation angle _θm calculated by the rotation angle calculation unit 49 by the reduction ratio N, thereby dividing the rotor rotation angle _θm into the rotation angle (actual steering angle) θ of the output shaft 9. Convert.

The assist control unit 41 sets a target assist torque Tm _,mc, which is a target value of assist torque required for manual operation. The assist control unit 41 sets target assist torques Tm _{, mc} based on the steering torque _Td detected by the torque sensor 12 and the vehicle speed V detected by the vehicle speed sensor 24 . A setting example of the target assist torque Tm _,mc with respect to the steering torque _Td is shown in FIG.

The target assist torque Tm _,mc takes a positive value with respect to a positive value of the steering torque _Td , and causes the electric motor 18 to generate a steering assist force for left steering. Also, the target assist torque Tm _,mc takes a negative value with respect to a negative value of the steering torque _Td , and causes the electric motor 18 to generate a steering assist force for rightward steering. The target assist torque Tm _,mc is set such that its absolute value increases as the absolute value of the steering torque _Td increases. The target assist torque Tm _,mc is set such that its absolute value decreases as the vehicle speed V detected by the vehicle speed sensor 24 increases.

Based on the target steering angle θ _cmda given from the host ECU 201 and the actual steering angle θ calculated by the reduction ratio dividing unit 50, the angle control unit 42 calculates a target angle control required for angle control (steering angle control). Set the torque Tm _,ac . Details of the angle control unit 42 will be described later.

The compensation target load estimator 43 calculates the steering torque _Td detected by the torque sensor 12, the actual steering angle θ calculated by the reduction ratio divider 50, and the target motor torque _Tm set by the shared controller 44. Estimate the load to be compensated T _lem based on . As will be described later, based on the angle control target torque T _m,ac set by the angle control unit 42 and the compensation target load T _lem estimated by the compensation target load estimation unit 43, the motor necessary for automatic steering is determined. A target automatic steering torque T _m,ad (see FIG. 8), which is a torque target value, is calculated. The details of the compensation target load estimator 43 will be described later.

The shared control unit 44 stores a target assist torque Tm _,mc set by the assist control unit 41, a target torque for angle control Tm, _ac set by the angle control unit 42, and a target torque Tm,ac for angle control which is calculated by the angle control unit 42. and the compensation target load T _lem estimated by the compensation target load estimator 43 are input. The shared control section 44 calculates the target motor torque _Tm based on these inputs. Details of the shared control unit 44 will be described later.

The target motor current calculation unit 45 calculates the target motor current I _cmd by dividing the target motor torque T _m calculated by the shared control unit 44 by the torque constant K _t of the electric motor 18 .

A current deviation calculator 46 calculates a deviation ΔI (=I _cmd −I) between the target motor current I _cmd obtained by the target motor current calculator 45 and the motor current I detected by the current detection circuit 32 .

The PI control unit 47 performs PI calculation (proportional integral calculation) on the current deviation ΔI calculated by the current deviation calculation unit 46 to drive the motor current I flowing through the electric motor 18 to the target motor current I _cmd . Generate a command value. The PWM control unit 48 generates a PWM control signal having a duty ratio corresponding to the drive command value, and supplies it to the drive circuit 31 . As a result, electric power corresponding to the drive command value is supplied to the electric motor 18 .

The angle control section 42, the compensation target load estimation section 43, and the shared control section 44 will be described in detail below.

FIG. 4 is a block diagram showing the configuration of the angle control section 42. As shown in FIG.

The angle control section 42 includes a low-pass filter (LPF) 61 , a feedback control section 62 , a feedforward control section 63 , a torque addition section 64 and a reduction ratio division section 65 .

The low-pass filter 61 performs low-pass filter processing on the target steering angle θ _cmda given from the host ECU 201 . The target steering angle θ _cmd after low-pass filtering is applied to feedback control section 62 and feedforward control section 63 .

The feedback control section 62 is provided to bring the actual steering angle θ calculated by the reduction ratio dividing section 50 (see FIG. 2) closer to the target steering angle θ _cmd . The feedback controller 62 includes an angular deviation calculator 62A and a PD controller 62B. The angle deviation calculator 62A calculates a deviation Δθ (=θ _cmd −θ) between the target steering angle θ _cmd and the actual steering angle θ calculated by the speed reduction ratio divider 50 . The angular deviation Δθ calculated by the angular deviation calculator 62A is provided to the PD controller 62B and also to the shared controller 44 .

The PD control section 62B calculates the feedback control torque _Tfb by performing PD calculation (proportional differential calculation) on the angular deviation Δθ calculated by the angular deviation calculating section 62A. Specifically, the PD control section 62B includes a proportional processing section 111, a differential processing section 112, a proportional gain multiplying section 113, a differential gain multiplying section 114, and an adding section 115. FIG.

The proportional gain multiplication unit 113 multiplies the angle deviation Δθ proportionally processed by the proportional processing unit 111 by the proportional gain _KP . Differential gain multiplication section 114 multiplies the angle deviation Δθ differentiated by differential processing section 112 by differential gain _KD . Addition section 115 calculates feedback control torque _Tfb by adding the multiplication results of proportional gain multiplication section 113 and differential gain multiplication section 114 . The feedback control torque T _fb is applied to the torque addition section 64 .

The feedforward control section 63 is provided to compensate for the response delay due to the inertia of the electric power steering system 1 and improve the control response. Feedforward control section 63 includes an angular acceleration calculation section 63A and an inertia multiplication section 63B. The angular acceleration calculator 63A calculates a target angular acceleration d ² θ _cmd /dt ² by second-order differentiating the target steering angle θ _cmd . Inertia multiplier 63B multiplies target angular acceleration d ² θ _cmd /dt ² by inertia J of electric power steering system 1 to obtain feedforward torque T _ff (=J·d ² θ _cmd /dt ² ). Calculate. Inertia J is obtained from a physical model of the electric power steering system 1, for example. The feedforward torque _Tff is given to the torque adder 64 as an inertia compensation value.

The torque addition unit 64 calculates the target steering torque for angle control (T _fb +T _ff ) by adding the feedforward torque T _ff to the feedback control torque T _fb . As a result, the target steering torque for angle control (the target torque for the output shaft 9) whose inertia is compensated is obtained. As a result, highly accurate motor control (steering angle control) can be performed.

The target steering torque for angle control (T _fb +T _ff ) is given to the reduction ratio dividing section 65 . The reduction ratio dividing unit 65 divides the target steering torque for angle control (T _fb +T _ff ) by the reduction ratio N to calculate the target torque for angle control T _m,ac (the target torque for the electric motor 18). This angle control target torque Tm _,ac is given to the shared control section 44 (see FIG. 2).

FIG. 5 is a block diagram showing the configuration of the compensation target load estimator 43. As shown in FIG.

The compensation target load estimation unit 43 includes a reduction ratio multiplication unit 71 , a disturbance torque estimation unit (disturbance observer) 72 , a subtraction unit 73 , and a reduction ratio division unit 74 .

A reduction ratio multiplication unit 71 multiplies the target motor torque _Tm set by the shared control unit 44 by the reduction ratio N to obtain the target steering torque N· _Tm acting on the output shaft 9 from the target motor torque _Tm− . Convert to

The disturbance torque estimator 72 estimates a non-linear torque (disturbance torque: torque other than motor torque) generated as a disturbance in a plant (controlled object (motor driven object)). _{The disturbance torque estimator 72 calculates a disturbance torque (disturbance load) T lc ,} a steering angle θ, and a steering An angular differential value (angular velocity) dθ/dt is estimated. In the following, estimated values of disturbance torque T _lc , steering angle θ, and steering angle differential value (angular velocity) dθ/dt may be represented by ̂T _lc , ̂θ, and d̂θ/dt, respectively.

The subtracting unit 73 subtracts the steering torque _Td detected by the torque sensor 12 from the disturbance torque _Tlc estimated by the disturbance torque estimating unit 72, thereby calculating the compensation target applied to the output shaft 9 (reduction gear 19). Calculate the load T _le (=T _lc −T _d ). The reduction ratio division unit 74 divides the compensation target load T _le calculated by the subtraction unit 73 by the reduction ratio N, thereby dividing the compensation target load T _lem applied to the motor shaft of the electric motor 18 via the speed reducer 19. Calculate. The load to be compensated T _lem calculated by the reduction ratio dividing section 74 is provided to the shared control section 44 .

The disturbance torque estimator 72 will be described in detail. The disturbance torque estimator 72 is composed of a disturbance observer that estimates the disturbance torque T _lc , the steering angle θ, and the angular velocity dθ/dt using, for example, the physical model 101 of the electric power steering system 1 shown in FIG. .

This physical model 101 includes a plant (an example of a motor driven object) 102 including an output shaft 9 and a worm wheel 21 fixed to the output shaft 9 . A steering torque _Td is applied to the plant 102 from the steering wheel 2 through the torsion bar 10 . Further, the plant 102 is provided with a road load torque _Trl from the steered wheel 3 side, and a part _Tf1 of the friction torque _Tf due to the friction of the rack-and-pinion mechanism or the like. Further, the plant 102 is provided with a target steering torque N· _Tm via the worm gear 20, and is provided with a portion _Tf2 of the friction torque _Tf by friction between the worm wheel 21 and the worm gear 20, or the like. Here, T _f =T _f1 +T _f2 .

Assuming that the inertia of the plant 102 is J, the equation of motion for the inertia of the physical model 101 is represented by the following equation (1).

d ² θ/dt ² is the acceleration of plant 102 . N is the speed reduction ratio of the speed reducer 19 . _Tlc indicates disturbance torque other than the motor torque applied to the plant 102 . In this embodiment, the disturbance torque _Tlc is considered to mainly include the steering torque _Td , the road load torque _Trl , and the friction torque _Tf .

A state equation for the physical model 101 of FIG. 6 is represented by the following equation (2), for example.

In the above equation (2), x is a state variable vector. In equation (2) above, _u1 is a known input vector. In equation (2) above, _u2 is an unknown input vector. In the above equation (2), y is the output vector (measured value). In equation (2) above, A is a system matrix. In equation (2) above, _B1 is the first input matrix. In equation (2) above, _B2 is the second input matrix. In equation (2) above, C is the output matrix. In the above equation (2), D is a feedthrough matrix.

We extend the above state equation to a system that includes the unknown input vector _u1 as one of the states. The state equation of the extended system (extended state equation) is represented by the following equation (3), for example.

In the above equation (3), x _e is the state variable vector of the extended system and is expressed by the following equation (4).

In the above equation (3), A _e is the extended system matrix. In the above equation (3), B _e is the known input matrix of the extended system. In the above equation (3), C _e is the output matrix of the extended system.

A disturbance observer (extended state observer) represented by the following equation (5) is constructed from the extended state equation of equation (3).

In equation (5), ̂x _e represents an estimate of x _e . Also, L is an observer gain. Also, ^y represents the estimated value of y. ^x _e is represented by the following equation (6).

̂θ is an estimate of θ, and _̂Tlc is an estimate of _Tlc .

The disturbance torque estimator 72 calculates the state variable vector _̂xe based on the equation (5).

FIG. 7 is a block diagram showing the configuration of the disturbance torque estimator 72. As shown in FIG.

The disturbance torque estimation unit 72 includes an input vector input unit 81, an output matrix multiplication unit 82, a first addition unit 83, a gain multiplication unit 84, an input matrix multiplication unit 85, a system matrix multiplication unit 86, a second It includes an addition section 87 , an integration section 88 and a state variable vector output section 89 .

The target steering torque N· _Tm calculated by the reduction ratio multiplication section 71 (see FIG. 5) is given to the input vector input section 81 . The input vector input unit 81 outputs an input vector _u1 .

The output of the integrator 88 is the state variable vector ̂x _e (see equation (6) above). At the start of computation, an initial value is given as the state variable vector _̂xe . The initial value of the state variable vector ̂x _e is 0, for example.

A system matrix multiplier 86 multiplies the state variable vector ̂x _e by the system matrix A _e . The output matrix multiplier 82 multiplies the state variable vector ̂x _e by the output matrix C _e .

The first adder 83 calculates the output (C _e ·̂x _e ). That is, the first adder 83 calculates the difference (y−̂y) between the output vector y and the output vector estimated value ̂y (=C _e ·̂x _e ). The gain multiplier 84 multiplies the output (y−̂y) of the first adder 83 by the observer gain L (see the above equation (5)).

The input matrix multiplication unit 85 multiplies the input vector u1 output from the input vector input unit ₈₁ by the input matrix _Be . The second adder 87 outputs the input matrix multiplier 85 output (B _e ·u ₁ ), the system matrix multiplier 86 output (A _e ·̂x _e ), and the gain multiplier 84 output (L(y −^y)) is added to calculate the differential value d^x _e /dt of the state variable vector. The integrator 88 calculates the state variable vector ̂x _e by integrating the output (d̂x _e /dt) of the second adder 87 . A state variable vector output unit 89 outputs an estimated disturbance torque value ̂T _lc , an estimated steering angle value ̂θ, and an estimated angular _velocity value d̂θ/dt based on the state variable vector ̂xe.

A general disturbance observer consists of an inverse model of the plant and a low-pass filter, unlike the extended state observer described above. The equation of motion of the plant is expressed by Equation (1) as described above. Therefore, the inverse model of the plant is the following equation (7).

Inputs to a general disturbance observer are J·d ² θ/dt ² and T _m , and are greatly affected by noise of the rotation angle sensor 23 because the second derivative of the actual steering angle θ is used. On the other hand, in the extended state observer of the above-described embodiment, the disturbance is integrated according to the difference (y - y) between the estimated steering angle value ^θ estimated from the motor torque input and the actual steering angle θ. Since the torque is estimated, the noise effect due to differentiation can be reduced.

FIG. 8 is a block diagram showing the configuration of the shared control section 44. As shown in FIG.

The shared control unit 44 includes an absolute value calculation unit 91, a division unit 92, a β calculation unit 93, an α calculation unit 94, a limiter 95, a subtraction unit 96, an α multiplication unit 97, and a β multiplication unit 98. , and an adder 99 . Limiter 95 is an example of a limit processor of the present invention.

The absolute value calculator 91 calculates the absolute value |Δθ| of the angular deviation Δθ. The division unit 92 divides the absolute value |Δθ| of the angular deviation Δθ calculated by the absolute value calculation unit 91 by a preset shared control effective angular deviation width (hereinafter simply referred to as “effective angular deviation width W”). By doing so, the weight calculation variable |Δθ|/W is calculated. Note that W>0.

The β calculator 93 calculates the weighting factor β based on the following equation (8). That is, the β calculator 93 calculates the weighting factor β using the saturation function sat _0,1 (|Δθ|/W) defined by the following equation (8). The saturation function sat _0,1 (|Δθ|/W) is calculated using the angular deviation Δθ, which is an example of "a value that changes according to the driver input".

That is, the β calculator 93 outputs 1 if |Δθ|/W is greater than 1, as indicated by the solid broken line in FIG. Further, if |Δθ|/W is equal to or greater than 0 and equal to or less than 1, the β calculation unit 93 outputs the calculation result of |Δθ|/W. Therefore, the weighting factor β takes a value of 0 or more and 1 or less.

The α calculator 94 calculates the weighting factor α by subtracting β from 1. That is, the α calculator 94 outputs 0 if |Δθ|/W is greater than 1, as indicated by the dashed broken line in FIG. Further, if |Δθ|/W is equal to or greater than 0 and equal to or less than 1, the α calculation unit 94 outputs a calculation result of {1−(|Δθ|/W)}. Therefore, the weighting factor α takes a value of 0 or more and 1 or less.

The limiter 95 sets the angle control target torque T _m,ac set by the angle control section 42 between a predetermined lower limit saturation value T _min (T _min <0) and an upper limit saturation value T _max (T _max >0). limit to In this embodiment, T _min =−T _max . Specifically, the limiter 75 calculates the target torque for angle control sat _Tmin,Tmax (Tm _,ac ) after the limiting process based on the following equation (9).

As shown in FIG. 10, the limiter 95 controls the angle control target torque Tm _,ac when the angle control target torque Tm,ac is equal to or higher than the lower limit saturation value _Tmin and equal to or lower than the upper limit saturation value _{Tmax .} is output as is. Further, the limiter 75 outputs the lower limit saturation value _Tmin if the angle control target torque Tm _,ac is less than the lower limit saturation value _Tmin . Further, the limiter 75 outputs the upper limit saturation value Tmax when the angle control target torque Tm _,ac is larger than _the upper limit saturation value _Tmax .

The limiter 95 is provided so that the driver can easily cancel the automatic steering during the automatic steering. Specifically, when the driver performs a steering operation (steering intervention) to cancel automatic steering during automatic steering, the angle deviation Δθ increases. The absolute value of the control target torque Tm _,ac increases. When the absolute value of the angle control target torque Tm _,ac increases, the steering reaction force when the driver intervenes in steering increases, making it difficult for the driver to intervene in steering. Therefore, a limiter 95 is provided to prevent the absolute value of the angle control target torque Tm _,ac from becoming too large.

The subtraction unit 96 subtracts the compensation target load T _lem estimated by the compensation target load estimating unit 43 (see FIG. 2) from the angle control target torque sat _{Tmin, Tmax} (T _{m, ac} ) after the limit processing by the limiter 95. By subtracting, the target automatic steering torque T _m,ad (=sat _{Tmin, Tmax} (T _{m, ac} )−T _lem ) is calculated. As a result, the target automatic steering torque _{Tm,ad in which} the road load torque _Trl and the friction torque _Tf are compensated is obtained.

The α multiplier 97 multiplies the target automatic steering torque (sat _{Tmin, Tmax} (T _{m, ac} )−T _lem ) calculated by the subtractor 96 by the weighting factor α calculated by the α calculator 94. , α·(sat _{Tmin, Tmax} (T _{m, ac} )−T _lem ).

The β multiplication unit 98 multiplies the target assist torque _Tm,mc set by the assist control unit 41 (see FIG. 2) by the weighting factor β calculated by the β calculation unit 93, thereby obtaining β·Tm _, Compute _mc .

The adder 99 adds α·(sat _{Tmin, Tmax} (T _{m, ac} )−T _lem ) calculated by the α multiplier 97 and β·T _m,mc calculated by the β multiplier 98. Thus, the target motor torque _Tm is calculated. The target motor torque _Tm is represented by the following equation (10).

T _m =α·(sat _{Tmin, Tmax} (T _{m, ac} )−T _lem )+β·T _{m, mc} (10)
That is, the shared control unit 44 weights and adds the target automatic steering torque (sat _{Tmin, Tmax} (T _{m, ac} ) - T _lem ) and the target assist torque T _{m, mc} to obtain the target motor torque T _m . Calculate.

The weighting factor β for the target assist torque Tm _,mc is 1 when (|Δθ|/W)>1, and is (|Δθ|/W) when 0≦|Δθ|≦1. On the other hand, the weighting coefficient α for the target automatic steering torque (sat _{Tmin, Tmax} (T _{m, ac} )-T _lem ) is 0 when |Δθ|/W>1, and when 0≤|Δθ|/W≤1 (1−|Δθ|/W).

Therefore, when |Δθ|/W>1, β=1 and α=0, so T _m =T _m,mc . of the angle deviation _{.DELTA..theta} . As a result, steering is performed by manual steering.

When |Δθ|/W is zero, β=0 and α=1, so T _m =(sat _{Tmin, Tmax} (T _{m, ac} )−T _lem ). Thus, when the angular deviation Δθ is 0, steering is performed based on the target automatic steering torque (sat _{Tmin, Tmax} (T _{m, ac} )−T _lem ).

When |Δθ|/W is within the range of 0≤|Δθ|/W≤1, the smaller |Δθ|/W (the closer |Δθ| approaches zero), the smaller β and the α growing. On the other hand, the absolute value of the target automatic steering torque (sat _{Tmin, Tmax} (T _{m, ac} )-T _lem ) decreases as |Δθ| decreases. Moreover, the absolute value of the target assist torque Tm _,mc increases as the absolute value | _Td | of the steering torque _Td increases, regardless of the angular deviation Δθ.

Therefore, when |Δθ|/W is within the range of 0≦|Δθ|/W≦1, and |T _d | and |Δθ| are relatively small when the driver is not performing a steering operation, Steering will be performed primarily based on (sat _{Tmin, Tmax} (T _{m, ac} )-T _lem ). This enables steering by automatic steering.

When |Δθ|/W is within the range of 0≦|Δθ|/W≦1, when the driver performs a steering operation (steering intervention), |T _d | Steering is performed based on _{m and mc} . This enables steering by manual steering. At this time, |Δθ| increases and the absolute value |T _{m,ac |} of the angle control target torque T _m,ac increases. is restricted by the limiter 95, it is possible to suppress an increase in the steering reaction force when the driver intervenes in the steering, so that the driver can easily intervene in the steering.

|Δθ|/W is in the range of 0≦|Δθ|/W≦1, and if the degree of steering intervention is weakened while the driver is performing steering intervention, |T _d | is large. is changed from large to small, and |Δθ| also changes from large to small. As a result, based on the equation (10), the absolute value of the target assist torque Tm _,mc changes from a large state to a small state depending on the degree of steering intervention, and the target automatic steering torque (sat _{Tmin, Tmax} (Tm _{, ac} )-T _lem ) changes from small to large.

When the degree of steering intervention is strengthened while the driver is performing steering intervention, the respective values change in the opposite direction. Therefore, the driver can seamlessly and smoothly switch between a state in which the automatic steering is subjective and a state in which the driver's steering is subjective, simply by adjusting the degree of steering intervention without being conscious of the seams of switching. can be done.

In the above-described embodiments, automatic steering control and manual steering control can be performed using the same electric motor with relatively simple control. Further, when the absolute value of the angle deviation Δθ reaches the effective angle deviation width W, the target motor torque _Tm becomes equal to the target assist torque _Tm,mc. can be quickly switched to

Although the embodiments of the present invention have been described above, the present invention can also be implemented in other forms. For example, in the above-described embodiment, the β calculator 93 (see FIG. 8) calculates the weighting factor β using the saturation function sat _0,1 (|θ|/W)). However, the β calculator 93 may use the steering torque _Td to calculate the weighting factor β.

Specifically, the β calculator 93 may perform calculations based on a saturation function sat _0,1 (P) given by the following equation (11). The saturation function sat _0,1 (P) is calculated using the steering torque T _d , which is an example of "a value that changes according to the driver's input." In this case, the steering torque _Td detected by the torque sensor 12 is input to the shared control section 44, as indicated by the two-dot chain lines in FIGS.

P decreases when the steering wheel is released (T _d =0). In the steering wheel gripping state, P increases as the absolute value |T _d | of the steering torque increases.

The weighting factor β for the target assist torque Tm _,mc is 1 when P>1, and is P when 0≤P≤1. On the other hand, the weighting coefficient α for the target automatic steering torque (sat _{Tmin, Tmax} (T _{m, ac} )-T _lem ) is 0 when P>1 and (1-P) when 0≤P≤1.

Therefore, when P>1, β=1 and α=0, so T _m =T _m,mc . As a result, when the absolute value |T _d | of the steering torque increases, steering is performed based on the target assist torque T _m,mc . As a result, steering is performed by manual steering.

When P<0, β=0 and α=1, so T _m =(sat _{Tmin, Tmax} (T _{m, ac} )−T _lem ). Thus, when the absolute value |T _d | of the steering torque is zero, steering is performed based on the target automatic steering torque (sat _{Tmin, Tmax} (T _{m, ac} )−T _lem ).

When P is within the range of 0≤P≤1, α increases as P (=β) decreases. Therefore, the ratio of the target automatic steering torque (sat _{Tmin, Tmax} (T _{m, ac} )-T _lem ) to the target motor torque T _m increases as P decreases. Conversely, the ratio of the target assist torque _{Tm ,mc} to the target motor torque Tm increases as the absolute value | _Td | of the steering torque _Td increases, that is, as P increases.

Therefore, when P is within the range of 0≦P≦1, the absolute value |T _{d |} Steering is performed based on _{Tmin, Tmax} (T _{m, ac} )-T _lem ). This enables steering by automatic steering.

When P is within the range of 0≦P≦1, when the driver performs a steering operation (steering intervention), the absolute value |T _d | of the steering torque T _d increases _{. , mc} . This enables steering by manual steering. At this time, |Δθ| increases and the absolute value |T _{m,ac |} of the angle control target torque T _m,ac increases. is restricted by the limiter 95, it is possible to suppress an increase in the steering reaction force when the driver intervenes in the steering, so that the driver can easily intervene in the steering.

When P is within the range of 0≦P≦1, if the degree of steering intervention is weakened while the driver is performing steering intervention, the absolute value |T _d | of the steering torque T _d is large. change to a smaller state. Therefore, P (=β) also changes from a large state to a small state, and α changes from a small state to a large state. As a result, based on the equation (10), the ratio of the target assist torque _{Tm ,mc} to the target motor torque Tm decreases according to the degree of steering intervention, and the target automatic steering torque (sat _{Tmin, Tmax} (Tm _{, ac} )-T _lem ) increases.

When the degree of steering intervention is strengthened while the driver is performing steering intervention, the respective values change in the opposite direction. Therefore, the driver can seamlessly and smoothly switch between a state in which the automatic steering is subjective and a state in which the driver's steering is subjective, simply by adjusting the degree of steering intervention without being conscious of the seams of switching. can be done.

Further, the β calculator 93 may calculate the weighting factor β using a saturation function sat _0,1 (Q _n ) given by the following equation (12). The saturation function sat _0,1 (Q _n ) is calculated using the steering torque T _d , which is an example of "a value that changes according to the driver's input". In this case also, the steering torque _Td detected by the torque sensor 12 is input to the shared control section 44, as indicated by the two-dot chain lines in FIGS.

In equation (12), Q _n indicates the current value of Q, and Q _n−1 indicates the previous value of Q. |T _d(n) | indicates the current value of the absolute value of the steering torque T _d .

When the steering wheel is released (T _d =0), Q _n decreases. In the steering wheel gripping state, Q _n increases as the absolute value |T _d | of the steering torque increases. Therefore, in this case as well, the same effects as when the weighting factor β is calculated based on the saturation function shown by equation (11) are obtained.

In the above-described embodiment, the angle control target torque Tm _,ac set by the angle control unit 42 is set to the lower limit saturation value _Tmin and the upper limit saturation value _Tmax so that the driver can easily release the automatic steering. A limiter 95 (see FIG. 8) is provided to limit the interval between . However, instead of the limiter 95, a gain control section 66 for controlling the feedback gain of the PD control section (see FIG. 4) may be provided as indicated by the chain double-dashed line in FIG. The gain control section 66 is an example of the limit processing section of the present invention.

In this embodiment, the gain control unit 66 controls the proportional gain _KP and the differential gain _KD based on values that change according to the driver input, thereby increasing the target torque Tm _,ac for angle control during steering intervention. Suppress the absolute value from becoming too large.

As the “value that changes according to the driver input” used in the gain control section 66, for example, the angular deviation Δθ, the steering torque _Td, and the like can be used. However, the "value that changes according to the driver input" used in the gain control unit 66 is preferably a different value from the "value that changes according to the driver input" used for the calculation of β.

11 and 12 show setting examples of the proportional gain _KP and the differential gain _KD when the "value that changes according to the driver input" used in the gain control section 66 is the steering torque _Td .

Referring to FIG. 11, proportional gain K _P is set to a predetermined positive value K _P0 when absolute value |T _d | of steering torque is zero. The proportional gain K _P is set to a positive predetermined value K _P1 smaller than K _P0 when the absolute value |T _d | of the steering torque is greater than or equal to a predetermined value A ₁ (A ₁ >0). When the absolute value |T _d | of the steering torque is in the range of 0 to A ₁ , the proportional gain K _P is set according to the characteristic of decreasing as |T _d | increases in the range from K _P0 to K _P1 .

Referring to FIG. 12, differential gain K _D is set to a predetermined positive value K _D0 when absolute value |T _d | of steering torque is zero. When the absolute value |T _d | of the steering torque is greater than or equal to a predetermined value B ₁ (B ₁ >0), the differential gain K _D is set to a positive predetermined value K _D1 smaller than K _D0 . When the absolute value |T _d | of the steering torque is in the range of 0 to B ₁ , the differential gain _KD is set according to the characteristic of decreasing as |T _d | increases in the range from K _D0 to K _D1 .

When the driver intervenes in steering during automatic steering, the absolute value of the angle deviation Δθ increases, the absolute value of the angle control target torque _Tm,ac increases, and the steering reaction force increases. It becomes difficult to perform steering intervention. However, when the steering intervention increases the absolute value of the steering torque _Td , the gain controller 66 reduces the proportional gain _KP and the differential gain _KD . As a result, the responsiveness of the angle control target torque _Tm,ac set by the angle control section 42 is lowered, so that the absolute value of the angle control target torque _Tm,ac can be suppressed from becoming excessively large.

In the setting examples of FIGS _. 11 and 12, the absolute value of the steering torque _Td is used on the horizontal axis. , 12, the saturation function sat _0,1 (P) defined by the above equation (11), the saturation function sat _0,1 (Q _n ) defined by the above equation (12), etc. may be used. . Also, when the angular deviation Δθ is adopted as the “value that changes according to the driver input”, the absolute value of the angular deviation Δθ can be used on the horizontal axis of FIGS.

Further, in the above-described embodiment, the angle control section 42 includes the feedforward control section 63, but the feedforward control section 63 may be omitted.

Further, in the above-described embodiment, the compensation target load _Tle includes the road load torque _Trl and the friction torque _Tf , but may include only one of them.

In addition, the load to be compensated _Tle may include inertia torque applied to the output shaft 9 by the inertia force of the constituent members of the torque transmission path from the torsion bar 10 to the tire.

Although the embodiments of the present invention have been described in detail, these are merely specific examples used to clarify the technical content of the present invention, and the present invention should be construed as being limited to these specific examples. should not, the scope of the invention is limited only by the appended claims.

This application corresponds to Japanese Patent Application No. 2017-230561 filed with the Japan Patent Office on November 30, 2017, the entire disclosure of which is incorporated herein by reference.

REFERENCE SIGNS LIST 1 electric power steering device 3 steered wheels 4 steering mechanism 18 electric motor 41 assist control section 42 angle control section 43 compensation target load estimation section 44 shared control section 61 ... low-pass filter (LPF), 62 ... feedback control section, 63 ... feedforward control section, 64 ... torque addition section, 66 ... gain control section, 201 ... host ECU, 202 ... motor control ECU

Claims (5)

an electric motor that applies a steering force to a steering mechanism of the vehicle;
a first setting unit that sets a target assist torque according to the steering torque;
a second setting unit that sets a target torque for angle control for bringing the angular deviation between the target steering angle and the actual steering angle closer to zero;
a limit processing unit that limits the target torque for angle control set by the second setting unit;
a first calculation unit that calculates a target automatic steering torque using the angle control target torque after the limit processing by the limit processing unit;
A second calculation for calculating a target motor torque, which is a target value of the motor torque of the electric motor, by weighting addition of the target automatic steering torque and the target assist torque according to a value that varies according to a driver input. and a steering system for a vehicle. 2. The limit processing unit according to claim 1, wherein the target torque for angle control set by the second setting unit is configured to be limited between a predetermined upper limit value and a predetermined lower limit value. Vehicle steering system. The second setting unit includes a feedback control unit for bringing the angular deviation closer to zero,
The limit processing unit limits the target torque for angle control set by the second setting unit by controlling a feedback gain of the feedback control unit based on a value that changes according to a driver input. 2. The vehicle steering system of claim 1, comprising: The vehicle steering system according to any one of claims 1 to 3, wherein the value that changes according to the driver's input is the steering torque or the angular deviation. The value that varies according to the driver input is the steering torque or the angular deviation. 4. The vehicle steering system according to claim 3, wherein the value that changes with the change is different.

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